Xylanases (endo-β-1,4-xylanase, EC 3.2.1.8) hydrolyze internal β-1,4-xylosidic linkages in xylan to produce smaller molecular weight xylose and xylo-oligomers. Xylans are polysaccharides formed from β-1,4-glycoside-linked D-xylopyranoses. Xylanases are very useful in multiple commercial applications, including for dough preparation or bread product preparation fruit and vegetable processing, breaking down agricultural waste, manufacturing animal feed as well as in lignocellulose pretreatment and pulp and paper production. Cellulose and hemicellulose materials which can be converted into fermentable sugars are considered a very useful and under-utilized source of renewable biomass materials. Individual β-1,4-glucose chains once synthesized, self-associate through hydrogen bonding to form semi-crystalline cellulose microfibrils (cellulose). The cellulose microfibrils are embedded in a polysaccharide matrix formed of hemicelluloses such as xylan, galactoglucomannan and xyloglucan all of which may be associated with other lower abundance biomass polysaccharides such as arabinans, mannans; pectins including galacturonans and galactans and various other β-1,3 and β-1,4 glucans all of which are dependent upon the plant source and the cellulosic tissue in question. The hemicellulose matrix is also typically surrounded and cross linked with polyphenolic lignins. From the tight interactions that exist between cellulose, hemicellulose and lignin, it is very difficult and expensive to break down this recalcitrant matrix of biomass to yield desired mixtures of oligosaccharides or fermentable simple sugars.
The primary hemicellulose from hardwood and crop residues is a glucuronoxylan (GX) consisting of a chain of β-1,4-linked xylose residues randomly substituted with α-1,2-linked glucuronic acid (GA) residues. Frequency of substitution has been shown to be as high as 1 GA for every 6 xyloses. In hardwoods, unaltered GX is additionally acetylated to a high degree on the O-2 or O-3 (or O-2 and O-3) hydroxyl positions. Commercial extraction of these polysaccharides typically is done under alkaline conditions which deacetylates these polysaccharides. This is the form of GX commonly used for laboratory studies. Other lower yielding extraction procedures must be implemented to obtain a glucuronoacetylxylan polysaccharide. Xylan is the second most abundant hemicellulose in softwood species next to galactoglucomannan, accounting for just less than half of the total hemicellulose. This source of xylan is in the form of glucuronoarabinoxylan with periodic GA substitutions and α-1,2-linked arabinofuranose substitution on the O-2 or O-3 (or O-2 and O-3) hydroxyl positions of xylose. Xylans from other sources such as grains (wheat, WAX) typically consist of an arabinoxylan, having patterns of arabinofuranose substitution similar to softwoods, but lacking the GA substitution.
The glycosyl hydrolase (GH) family 30 (GH30) enzymes (Cantarel, et al., 2009) have recently been redefined (St. John, et al., 2010). The new family composition consists of eight subfamilies that can be assigned into two structurally and phylogenetically distinguishable groups. Biochemical and structural studies have shown the enzymes in subfamily 8 to have unique characteristics in the degradation of the hemicellulosic polymer glucuronoxylan (St. John, et al., 2006; Vrsanska, et al., 2007; Hurlbert & Preston, 2001).
Accordingly, a need exists for novel glycosyl hydrolase enzymes, compositions and methods of use which can more efficiently convert plant or other cellulosic or hemicellulosic materials into fermentable sugars.